On 1/15/25 5:12 PM, Jason Xing wrote:
Also, I need to set allow_direct_access to one as long as there is
"sock_ops.is_fullsock = 1;" in the existing callbacks.
Only set allow_direct_access when the sk is fullsock in the "existing" sockops
callback.
Only "existing"? Then how can the bpf program access those members of
the tcp socket structure in the current/new timestamping callbacks?
There is at least one sk write:
case offsetof(struct bpf_sock_ops, sk_txhash):
SOCK_OPS_GET_OR_SET_FIELD(sk_txhash, sk_txhash,
struct sock, type);
afaict, the kernel always writes sk->sk_txhash with the sk lock held. The new
timestamping callbacks cannot write because it does not hold the lock.
Otherwise, it needs another flag in bpf_sock_ops_kern to say read only or not.
imo, it is too complicated to be worth it.
It is fine for the new timestamping callbacks not able to access the tcp_sock
fields through the bpf_sock_ops. We are not losing anything. The accessible
tcp_sock fields through the bpf_sock_ops is limited and the bpf_sock_ops api is
pretty much frozen. The bpf prog should use the bpf_core_cast(skops->sk, struct
tcp_sock). The future UDP timestamping support will likely need to use the
bpf_core_cast anyway because we are not extending "struct bpf_sock_ops" for the
udp_sock specific fields.
